[Editor’s Note: Creepy. And ironic. Factory farming of swine and poultry helped to create the swine and bird flu, and now factory farming of chickens is what is producing the millions of doses of vaccine for H1N1. For more information visit OCA’s Flu Resource Center.]

PENNSYLVANIA DUTCH COUNTRY — Nestled in and around this scenic agricultural belt are secret facilities that don’t take kindly to visitors.

“Keep Out” reads a sign near the gated entrance at one site. Some of the stark, windowless warehouses require electronic pin codes and hazmat-style jumpsuits to enter. A sign on a metal gate ominously warns that it is a “Disease Control Area.” Trespassers could bring a swift response from police geared up to fight bio-terrorism.

These aren’t government labs, military facilities or weapons plants.

They are egg farms.

At clandestine farms across Pennsylvania, thousands of roosters and hens have been toiling away for months in confidential conditions normally reserved for important government ops. Their mission: Fertilize enough eggs to keep supplies of swine-flu vaccine flowing.

Fertilized chicken eggs are a central ingredient in the making of flu shots. They serve as miniature incubators that help the virus multiply before it is inactivated and turned into vaccine. As fears of a pandemic have grown in recent years, the U.S. government has helped finance the formation of extra chicken flocks to ensure enough eggs would be available for emergency vaccine production.

Sanofi-Aventis SA, a large vaccine maker, has been using as many as 600,000 eggs a day in its global swine-flu-vaccine production. GlaxoSmithKline PLC was using 800,000 a day at the peak of its production. Manufacturers get very few doses of swine-flu vaccine per egg — from less than one to four.

In 2005, the U.S. classified these chicken barns as part of the nation’s “critical infrastructure,” giving them a kind of top-secret status. The secrecy is owing to worries that flu-related egg farms could be targeted for terrorist attacks or struck by chicken-killing pathogens.

The government wanted a “secure system to protect these birds,” with “very strict conditions for the entry and exit of people and product,” said Robin Robinson, an official at the Department of Health and Human Services who masterminded the secret egg program. “If we had no vaccine now it would be a very bad thing.”